1. Field of the Invention
This invention relates to refractory bricks used to protect membrane boiler tubes, a suspended wall of such refractory bricks, and to a method for mounting refractory bricks used to protect membrane boiler tubes.
2. Description of the Prior Art
Boiler designs have boiler tubes running parallel at a predetermined distance from each other to carry liquids to be heated by the combustion within the boiler. Membrane boilers have a fin welded between adjacent boiler tubes resulting in an air-tight sealed enclosure. It is desirable in modern boiler design to have membrane boiler tube protection. In membrane boilers the welded fins prevent installation of refractory material which locks around the inside periphery of the boiler tube.
Murray, Jr., U.S. Pat. No. 2,167,901 teaches a boiler wall formed by tubes having high thermal conducting fins extending outward and substantially closing the space between the boiler tubes. The '901 patent teaches a furnace wall constructed of shaped refractories grouted in place or held in place by a plastic insulation outer layer and metal shell. The '901 patent does not teach a method for individually replacing refractories, nor does it teach any type of refractory suspension system.
Several patents teach methods for attaching refractories to furnace wall structures which have spaces open between the boiler tubes. Hitchcock, U.S. Pat. No. 1,202,386, teaches a method for installing mortise and tenon bricks between open boiler tubes. Tone, U.S. Pat. No. 1,775,414, Davey, U.S. Pat. No. 2,276,025, and Johnson, U.S. Pat. No. 1,876,301 teach refractories which interlock through spaces between the boiler tubes and depend upon access to more than one-half the peripheral surface of the boiler tubes.
Beck, U.S. Pat. No. 2,734,259 and Coe, U.S. Pat. No. 3,448,798 teach heat exchangers which provide improved thermal exchange from the tubes through the use of high thermal conductivity in association with the tubes. Saveker, U.S. Pat. No. 3,992,835, teaches improved core members suitable for use in composite structural elements.
Prior refractory designs which protect boiler tubes date back many decades. However, such designs do not accommodate the configurations of membrane-type boilers. Prior refractory designs can be used on boilers having an open space between the boiler tubes. In such prior designs, he refractory bricks fit into place through the open space and lock in back of the boiler tubes. Membrane-type boilers have no open spaces between the boiler tubes, therefore, such boilers do not accommodate prior refractory designs.
One established method for applying protection to membrane boiler tubes uses monolithic materials. A plurality of studs welded to the boiler tubes and fin membranes act as anchors to hold either gunned or trowelled into place monolithic materials. However, monolithic materials have proven unsatisfactory for adequate boiler tube protection. In contrast with monolithic materials, pre-fired refractory products such as refractory bricks have greater density, provide better heat transfer to the boiler tubes, have better resistance to slag adhesions, have better resistance to erosion, and unlike monolithic materials, require no curing in the field.
Other prior designs used to apply pre-fired refractory bricks to a membrane boiler use a threaded stud, welded to the boiler tube or fin membrane, and a refractory brick having a through hole. The threaded stud extends through the hole in the brick and a nut fastens on the threaded stud to hold the brick in place. A brick with a through hole causes difficulties such as heat loss and erosion. Another prior design uses two bars welded to and extending angularly upwardly and outwardly from the membrane fin of the boiler wall. Refractory bricks used in such design have matching upwardly and outwardly angled recesses in the face of the refractory brick. The angled recesses allow the refractory bricks to slide onto the two bars extending from the boiler wall. Such design requires critical placement of the two bars for proper support. In addition, the refractory bricks do not interlock in place nor can they be individually replaced.